Here is the key [to Doing it right]. We need to let Apt know which is our preferred update repository. That information comes from the /etc/apt/apt.conf file. If it doesn't exist, create it. It needs to include this line:

With that in place, aptitude will first look at testing, and if it sees the program you have identified, it will look no further. In our scenario, since we know we want our application from Unstable, our command will be: